adum, Tomas had a problem 1068 posted for which O-O is the first move of the solution.
1. I couldn't edit the problem to 1 O-O.
2. O-O was not allowed as a first move when trying to solve the problem.
3. I sandboxed the problem.
4. Solution is 1. O-O Qf6 2.Rf3+ Qxf3 3.Qh6+ Qf4 4.Qxf4#
Lawrence